ABSTRACT
Two popular implementations of the control unit (hardwired control unit [HCU] and microprogrammed control unit [MCU]) were described in Chapter 6. The subsequent chapters provided the details of architectural features found in modern-day machines. Inclusion of any new feature into the architecture requires a corresponding enhancement to the control unit. The following parameters are usually considered in the design of a control unit:
With the advances in hardware technology, faster and more versatile processors are introduced to the market very rapidly. This requires that the design cycle time for newer processors must be as small as possible. Since the design costs must be recovered over a short life span of the new processor, they must be minimized. MCUs offer such exibility and low-cost redesign capabilities, although they are inherently slow compared with HCUs. This speed differential between the two designs is getting smaller, since in the current technology, the MCU is fabricated on the same integrated circuit (IC) (i.e., with the same technology) as the rest of the processor. We will concentrate on the popular speed-enhancement techniques used in contemporary machines in this chapter.
